Electromagnetic processes in silver isotopes

Peculiarities of electromagnetic interactions in silver isotopes are considered. Excited states of Ag isotopes are studied as a function of the mass number A = 95–117. Low-lying excited states reveal clear features that are specific for rotational spectra for the energies E < 4–5 MeV. In the energy domain above the nucleon separation threshold of 5–10 MeV, single-particle excited states overlap and produce a continuous spectrum. For energies E = 10–35 MeV, excitation of giant dipole resonance plays the most important role in Ag isotopes. Experimental data on the cross sections of photonuclear reactions in Ag isotopes are analyzed.     

Evaluation of the sulfate dynamics in groundwater by means of environmental isotopes

Elevated sulfate concentrations and their heterogeneous distribution in the drinking water catchment area Torgau-Mockritz (Germany) were investigated by means of multiple isotope signatures such as 834S, delta18O-H2O, deltaD, tritium, and 85K5r. delta34S values of the groundwater sulfate vary between -19...+ 37 per thousand CDT. No simple correlation exists between sulfate concentrations and delta34S. Superimposition of different sulfur sources and mobilization processes combined with a complicated groundwater movement create a complex distribution pattern. The oxidation of reduced sedimentary sulfur has to be regarded as a main source of dissolved sulfate at least regionally. Tritium and 14C data revealed that old groundwater can be excluded as source for high sulfate contents. Correlated temporal variations in the concentrations of tritium and sulfate are observed in deeper sampling positions. Highly variable delta18O and 8D, as detected in parts of the catchment area, indicate local influences of surface water infiltration into the aquifer. The spatial distribution of isotope signatures enables the identification of zones with descending younger water or hindered groundwater movement and hence provides useful hints for flow modeling.     

Using environmental isotopes 2H and 18O for identification of infiltration processes in floodplain ecosystems of the River Elbe

We examined a floodplain area in the middle section of the river Elbe Valley with regard to hydrogeological and hydrological processes using isotopic methods. Over two years, river water and groundwater have been analysed for temporal and spatial chemical and isotopic (delta2H and delta18O) changes. By these methods we assessed the flow dynamics of the river-groundwater infiltration system. At low and mean river stages there is a general hydraulic gradient from the higher areas at the margin of the valley towards the floodplain. During floods river water infiltrates into the adjacent aquifer not primarily through the river banks but first through surface water inflow from north to south, via depressions and gullies from the back of the floodplain. The early stage of river water infiltration is characterized by a sharp decrease in conductivity and in concentrations of SO4(2-) and Cl- in the hydraulically connected shallow aquifer. delta2H and delta18O values show a similar tendency. We observed a significant minimum in stable isotope ratios during the flood in March 1999. Using a simple mixing equation it was calculated that the groundwater in the upper, shallow aquifer consists of around 70% river water in the transition zone (well 13) during flooding.     

Two-nucleon transfer processes in the lead region

In the lead region a theoretical study of two-nucleon transfer processes is made with the help of the generator coordinate method. Both two-proton and two-neutron transfer reactions are described. The two-phonon pairing vibrational states in ²⁰⁸Pb are especially considered. Energies, relative cross sections and angular distributions are presented and compared, when possible, with experiments.     

Photonuclear reactions on mercury isotopes in the region of the giant-dipole-resonance energy

The induced-activity method is used to measure yields of photonuclear reactions induced in stable mercury isotopes by beams of bremsstrahlung photons whose spectra have the endpoint energies of 19.5 and 29.1 MeV. On the basis of a collective model, the partial cross sections and yields are calculated for photoproton and photoneutron reactions on these isotopes. The yields calculated theoretically are compared with their measured counterparts. The possibility for the production in photonuclear reactions of the bypassed nucleus ¹⁹⁶Hg, which cannot be formed in astrophysical r and s processes, is analyzed.     

Isomeric ratios in photonuclear reactions of molybdenum isotopes induced by bremsstrahlung in the giant dipole resonance region

We have determined the isomeric ratios of isomeric pairs ^97m,gNb, ^95m,gNb and ^91m,gMo produced in ⁹⁸Mo(γ, p)^97m,gNb, ⁹⁶Mo(γ, p)^95m,gNb and ⁹²Mo(γ, n)^91m,gMo photonuclear reactions in the giant dipole resonance (GDR) region by the activation method. The results were analyzed, discussed and compared with the similar data from literature to examine the role of excitation energy, neutron configuration, channel effect and direct and pre-equilibrium processes in (γ, p) photonuclear reactions. In this work the isomeric ratios for ^97m,gNb from 14 to 19 MeV, for ^195m,gNb from14 to 24 MeV except 20 and 23.5 MeV and for ^91m,gMo at 14 and 15 MeV are the first time measurements.     

Fluctuation processes in the surface region of indium antimonide

Amplitudes of fluctuations in the surface potential in MOS structures are studied as a function of the state of the semiconductor substrate surface, the measurement frequency, and the intensity of background illumination. It is established that the dominant noise in the depletion-weak inversion region is generation-recombination noise produced by recharging of a deep impurity in the indium antimonide surface layer. In the strong inversion region explosive noise may be dominant. The relationship of the latter to structural defects of the semiconductor substrate is clarified. A model is proposed for generation of explosive noise in MOS-structures, based on the assumption of microplasma breakdown of the space charge region with an impurity defect atmosphere and phase readjustments of the matrix and oxide material. It is concluded that it is possible to reduce explosive noise in MOS-structures.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 60–65, September, 1988.The authors express their gratitude to I. I. Fefelova and B. G. Plomip for preparation of the MOS-structures.     

Dynamic non-linear optical processes in semiconductors

In this article active non-linear optical effects in semiconductors are reviewed. These processes arise because of the dynamics of excited populations of charge carriers temporarily created in otherwise empty states when a beam of laser radiation is incident on the material. A large number of different effects have been observed in different semiconductor materials recently and the non-linearities cover a wide range of magnitudes both in time-scale and size of non-linearity. The theory and physical concepts relevant to these processes are described and experimental observations using both high power pulsed and low power c.w. lasers are reviewed. Applications in optical bistability, phase conjugation, optical gating and optoelectronic gating are discussed.     

Decay studies of Au isotopes in the mass number region 186–189

Internal conversion electrons and gamma-rays emitted in the decays of the neutron deficient gold isotopes with mass numbers 186–189 have been studied with a double focussing beta-ray spectrometer and a Ge(Li) detector. Multipolarities for the strongest transitions have been deduced. A revised level scheme for¹⁸⁹Pt is proposed. The half-lives of¹⁸⁶Au,¹⁸⁸Au and¹⁸⁹Au are found to be (10.7±0.5), (9.0±0.4) and (28.6±1.0) minutes respectively.     

Dynamic origin of the condensed state in real processes

The behavior of condensed systems losing equilibrium under an external action is considered. The interrelation of irreversible processes in such systems is studied under the conditions when this relation becomes nonlinear. The concepts developed here make it possible to analyze processes and to reveal self-organization mechanisms as examples in three dynamic effects: constant friction, resonance mode of thermoelastic martensite transformations, and chemical dispersion upon doping of metal alloys. A conclusion is drawn regarding enhancement of interrelation between micro- and macroprocesses required for optimizing external action in condensed systems.     

Dynamic processes in metal nanoparticles under irradiation

Dynamic processes occurring in a nanoscale metal object during the implantation of high-energy ions are studied in detail. It is shown that the elastic and thermoelastic lattice responses to irradiation form force factors considerably affecting the evolution of the defect-impurity system, which, in turn, leads to a decrease in the number of structural defects. Quantitative estimates of the spatial redistribution of defects resulting in their emergence on the surface are obtained. Such self-organization of nanoparticles under ionizing radiation forms a basis for the production of nanostructured radiation-resistant materials capable of sustaining a long-term intense radiation load.     

New neutron-rich isotopes in the scandium-to-nickel region,produced by fragmentation of a 500 MeV/u86Kr beam

We have measured production cross-sections of the new neutron-rich isotopes⁵⁸Ti,⁶¹V,⁶³Cr,⁶⁶Mn,⁶⁹Fe,⁷¹Co and neighbouring isotopes that have been identified as projectile fragments from reactions between a 500 MeV/u⁸⁶Kr beam and a beryllium target. The isotope identification was performed with the zero-degree magnetic spectrometer FRS at GSI, using in addition time-of-flight and energy-loss measurements. The experimental production cross-sections for the new nuclides and neighbouring isotopes are compared with an empirical parametrization. The resulting prospects for reaching even more neutron-rich isotopes, such as the doubly-magic nuclide⁷⁸Ni, are discussed.This work is part of the Ph.D. Thesis of M. Weber     

Dynamic anomaly in the glass transition region of orthoterphenyl

We report on incoherent and coherent neutron scattering results in the supercooled liquid and the glassy regime of the van der Waals fluido-terphenyl using the backscattering and spin echo technique, respectively. A critical comparison of both techniques is presented. The data are analysed in the time domain assuming that microscopic correlation times (τ) scale with the viscosity η according to τ(T)～η(T)/T. With this assumption we obtain an agreement with several predictions of mode coupling theory: the existence of a critical temperatureT _c is shown, independently for both incoherent and coherent data, by a cusp in the temperature dependence of the Debye-Waller factorf _Q (T). BelowT _c f_Q(T) follows the predicted \(\sqrt {T_c - T} \) behaviour yielding also theQ-dependence of the critical parametersf _Q ^c andh _Q . AboveT _c the α-process or structural relaxation can be well parametrized by a stretched exponential function. In accordance with theory the structural relaxation curves can also be described by a power law with a critical (von Schweidler) exponentb=0.525±0.10.     

Dynamic processes in helical electron beams in gyrotrons

The results of theoretical and experimental studies of collective processes in helical electron beams in gyrotron-type devices are generalized. Main attention is paid to low-frequency oscillations associated with the development of instability in the space charge trapped between the cathode and the magnetic mirror. The mechanism of evolution of instability is substantiated and the effect of oscillations on the main parameters of the electron flow determining its quality is analyzed. Data on the suppression of low-frequency oscillations and resulting enhancement of the gyrotron efficiency are considered.     

Particle momentum cut-off in inclusive processes in the region of large angles

It is shown that analyticity and unitarity lead to logarithmic cut-off of particle momentum detected in binary inclusive process in the region of large angles.     

Dynamic electromagnetic processes in micro-wires inferred from GMI-characteristics

The penetration depth of the skin-effect has been calculated for a specimen in the form of a piece of amorphous glass-coated magnetic micro-wire of the “non-magnetostrictive” composition Co₆₇Fe_3.85Ni_1.45Mo_1.7Si_14.5B_11.5 displaying large GMI effect. For these calculations a simple model was applied in which a rough assumption was made that the changes of the real component of the impedance are due only to changes in the effective cross-section of the wire for the AC-current. The evolution of the penetration depth with the applied DC-axial field and frequencies of the AC-current, flowing along the wire, is presented. The so-called Cole–Cole diagrams were also plotted for the same specimen. These diagrams, representing the measured impedance plotted in the complex plane, were obtained for axial DC-magnetic field of selected intensities and circular AC-field generated by an AC-current of various frequencies (1–30 MHz) flowing along the wire specimen. Analysis of the diagrams enabled one to characterize magnetization processes within the wire specimen and also to estimate the median relaxation time of these processes as well as a relative measure of the distribution of relaxation times.